1. Field of the Invention
The present invention relates to an elevator speed governor located on an elevator cage to detect overspeed of the elevator cage.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 5-147852 discloses an elevator speed governor, which is composed as follows. There is provided a link oscillating around a fulcrum provided on an elevator cage. A pair of permanent magnets has between them an induction conductor arranged in the hoistway in the elevating direction of the cage. The magnets and a back yoke are attached to one end of the link, and a balance weight, which is balanced with the moment of the permanent magnet and yoke, is attached to the other end of the link. An electromagnetic force is generated by an interaction between an eddy current, which is caused in an induction conductor by the magnetic flux of the permanent magnet according to the traveling of the cage, and the magnetic flux. The link is tilted by this electromagnetic force. By this tilt of the link, overspeed of the cage is detected.
Also, Japanese Unexamined Patent Publication No. 4-246079 discloses an elevator speed governor composed as follows. There is provided a roller which is pressed against a guide rail arranged in the hoistway in the elevating direction of the cage. When the cage is elevated, a rotary disc is rotated, and the overspeed of the cage is detected by displacement of a fly-weight attached to this rotary disc.
The conventional elevator is composed as described above. However, the following problems may be encountered in the conventional elevator. The electromagnetic force generated between the eddy current created in the induction conductor and the magnetic flux depends upon the electrical conductivity and magnetic permeability of the induction conductor. Therefore, errors are caused in the detection of the overspeed, for example, by the fluctuation of temperature. In the case where the guide rail is also used as an induction conductor, it is impossible to guarantee that the magnetic characteristic of the guide rail will be uniform, and the detecting motion fluctuates due to the fluctuation of the magnetic characteristic of the guide rail. In the case of detecting the overspeed by displacement of a fly-weight caused by a centrifugal force acting on the fly-weight arranged on the rotary the inertia of the rotational section is high, so that the response becomes slow. Further, when the cage speed is slow, intensity of the centrifugal force is low, and it impossible to detect the cage speed stably. Furthermore, slippage of the detecting roller may be caused by step portions at the connecting sections of the guide rails. Therefore, it is impossible to detect the overspeed stably.
The present invention has been accomplished to solve the above problems of the prior art. It is an object of the present invention to provide an elevator speed governor in which no change is caused in the detection of the overspeed by the fluctuation of the electromagnetic characteristic of an induction conductor and also by the fluctuation of temperature; and the overspeed can be stably detected even in the case of low cage speed.
The present invention provides an elevator speed governor comprising: a motion converting means for converting a traveling speed of a traveling section of an elevator into a rotational speed, the motion converting means being mounted on the traveling section of the elevator; an overspeed sensing means for sensing a rotational speed not less than a predetermined speed of the motion converting means; and an overspeed detecting means for detecting an overspeed of the traveling section so as to stop the traveling section, wherein the motion converting means includes permanent magnets supported by a rotational shaft of the motion converting means so that the magnets can be rotated integrally with the rotational shaft, and an eddy current is generated according to the traveling speed in an electric induction conductor, which is arranged in a traveling direction of the traveling section of the elevator, by an action of electromagnetic induction caused by the magnetic flux of the permanent magnets, so that a rotational torque is generated in the rotational shaft by the interaction between the eddy current and the magnetic flux.
The induction conductor is a guide rail arranged in the traveling passage.
The overspeed sensing means includes a fly-weight rotated integrally with the rotational shaft and displaced relatively to the rotational shaft by centrifugal forces created by the rotation of the rotational shaft.
The fly-weight supports the permanent magnets and composes a portion of the motion converting means.
The overspeed sensing means includes an oscillator sensing a change of a spatial distribution of the magnetic flux caused by the rotation of the motion converting means and oscillating by an amplitude according to the rotational speed.
The overspeed sensing means includes a power generating means for sensing a change of a spatial distribution of the magnetic flux caused by the rotation of the motion converting means and generating electric power according to the rotational speed.
The motion converting means includes a roller coming into contact with a guide rail arranged in the traveling passage and rotating according to the traveling speed.